1. Field of the Invention
This invention relates to a cutting tool, and more particularly to a quick-change cutting tool comprising a head portion supporting thereon a cutting insert or a tip having a cutting edge, and a shank portion on which the head portion is detachably mounted.
2. Description of the Prior Art
In the past, cutting tools were of one piece, i.e., a cutting edge was integrally formed on one end of a shank. Such a one-piece cutting tool is fixed to a machine such as a lathe at the other end portion of the shank. The one-piece cutting tool is disadvantageous in that the cutting tool must be indexed so that the cutting edge is correctly positioned with respect to the workpiece each time the tool is changed. Therefore, the tool changing operation requires a long time and adds to the processing cost of the workpiece.
Thus there has been proposed a cutting tool comprising a holder having a shank portion and a head portion, and a cutting insert which is received in a locator formed in the head portion and is detachably fixed therein. The cutting tool of this type is advantageous in that the cutting insert can be changed without removing the holder from the machine and the new cutting insert can be indexably or replaceably located with respect to the workpiece by the locator, whereby the time required to change the tool can be shortened. However when cuttings remain in the locator, the locator cannot properly function and therefore cuttings or chips must be completely removed from the locator in order to precisely locate the cutting insert with respect to the workpiece. This prevents substantial reduction of the tool changing time and limits the possibility of the tool's being changed by an automated system.
There has been proposed a cutting tool comprising a cutting head cartridge supporting thereon a cutting insert and a shank assembly which are releasably secured together by way of a joint. In this cutting tool, the cutting insert is changed along with the cartridge without removing the shank assembly from the machine. Therefore the cutting insert can be indexed with respect to the workpiece by properly locating the cartridge with respect to the shank assembly under the guidance of guide means in the joint. Since the joint is remote from the cutting edge of the cutting insert, the adverse affect of cuttings is not so significant in this tool, whereby the tool changing time can be substantially shortened. The cutting tool of this type is generally referred to as a "quick-change tool".
An example of a quick-change tool is disclosed in Japanese Unexamined Patent Publication No. 55(1980)-54104. The quick-change tool disclosed in this Japanese Unexamined Patent Publication comprises a cutting head cartridge and a shank assembly. The cutting head cartridge comprises a cartridge body and a cutting insert detachably mounted on the cartridge body. The cartridge body is provided with a receptacle portion on the rear end portion, the receptacle portion forming a part of the joint for detachably connecting the cutting head cartridge and the shank assembly. The shank assembly comprises a shank body having an axial bore and a draw bar member slidably received in the axial bore of the shank body. The draw bar member is provided on the front end with a plug portion which forms the joint together with the receptacle portion of the cutting head cartridge. The receptacle portion of the cartridge is in the form of a backwardly projecting channel member having a vertical groove which is substantially cylindrical in shape and opens backwardly through a slot narrower than the diameter of the groove. The plug portion of the draw bar member is in the form of a vertically extending enlarged cylindrical portion the diameter of which is smaller than that of the vertical groove of the receptacle portion and which is connected to the body of the draw bar member by way of a neck portion having a width slightly smaller than that of the slot of the receptacle portion. A vertically extending recess is formed in the front end face of the shank body and the front end of the axial bore from which the plug portion projects opens in the base of the recess. When the cartridge is mounted on the shank assembly, the draw bar member is drawn backwardly with the plug portion being received in the receptacle portion, whereby the receptacle portion of the cartridge is drawn into the recess in the front end face of the shank body with its rear end face being pressed against the base of the recess and at the same time the slot of the receptacle portion is resiliently expanded by way of the abutment between the inner surface of the groove adjacent to the slot and the outer surface of the plug portion adjacent to the neck portion. In this position, the lower surface of the receptacle portion rests on shoulders formed on opposite side walls of the recess of the shank body. Thus the cartridge is located with respect to the shank body axially by the abutment between the rear end face of the receptacle portion and the base of the recess, vertically by the abutment between the lower surface of the receptacle portion and the shoulders, and laterally by the resilient force of the side walls of the receptacle portion. The quick-change tool of the Japanese Unexamined Patent Publication identified above is satisfactory insofar as it permits quick change of the tool or the cutting head cartridge. However it has drawbacks in that the mounting rigidity or the rigidity of the joint portion of the cartridge and the shank assembly when the cartridge is mounted on the shank assembly is not sufficient especially in the direction of the principal component of the force exerted on the cutting insert during a cutting operation, and since the side walls of the receptacle portion must resist the expanding force exerted thereon, the thickness of the side walls must be large, which adds to the overall width of the tool. Further since the joint portion is exposed, chips may sometimes enter the joint portion to interfere with correct location of the cartridge with respect to the shank body.